Semiconductor lasers are generally made from light-emitting properties of III-V semiconductor materials. The term “III-V” herein refers to elements from group III to group V of the periodic table. Typical semiconductor lasers are composed of two components, an III-V active region to generate light and a silicon waveguide to carry the generated light. The two components are combined together by molecular O2 plasma-assisted wafer bonding procedure or alternatively by means of an adhesive die-to-wafer binding technique that applies benzocyclobutene (BCB) adhesive between the III-V active region and the silicon waveguide.
The molecular O2 plasma-assisted wafer bonding procedure is a hydrophilic bonding process that applies a thin oxide layer between the two components. The hydrophilic bonding process requires completely clean, smooth, and contamination-free bonding surfaces which are difficult to meet for high volume manufacturing. In the hydrophilic bonding process, the two components are combined to form a hybrid III-V silicon laser by annealing the two components at high temperature e.g., 300° C., for 40-60 minutes to form an intermediate-strength bond between the layer of the III-V active region and the silicon substrate. The process of annealing also requires channels to be made in the silicon component to diffuse hydrogen formed by the process of annealing. Any surface roughness or contamination between the bonding surfaces results in large unbounded areas causing the intermediate-strength bond. The alternative approach of using BCB adhesive between the III-V active region and the silicon region requires an additional fabrication process of applying the adhesive which changes the distance between the silicon waveguide and a multiple quantum well region of the III-V active region, thus impacting the performance of the hybrid III-V silicon laser.
FIG. 1A illustrates a cross-section of such prior art hybrid III-V silicon laser 100 in which the III-V active region 101 is bonded to the silicon region 102 at high temperature via a layer of oxide 103. The III-V active region 101 is formed from layers of III-V semiconductor materials 110 which do not include metal contacts 107 and 108. The III-V active region 101 generates the current that flows from the positive contact 108 towards the negative contact 107 when a potential difference is applied across the positive contact 108 and the negative contact 107. The current generated in the active region 101 further generates light which is channeled through a silicon waveguide 105. The waveguide 105 is confined to its position by regions 109 on either side of the waveguide 105. The light generated by the current forms a laser beam which can be used for optical communication.
The plasma activation process uses a thin oxide layer 103 between an Indium Phosphide (InP) layer 106 of the active region 101 and silicon layer 102. The silicon region 102 of FIG. 1A is a silicon-on-insulator (SOI) having a buried oxide layer 111 between a silicon substrate 112 and a silicon interface layer 113. The plasma activation process forms hydrogen bonds between water molecules. To complete the hydrogen bonds, the annealing process generates hydrogen molecules which diffuse either to the edge of the bonded surface or to vertical channels 104 connected to the buried oxide layer 111 which absorbs the hydrogen molecules.
The annealing process causes stress to the two regions 101 and 102. Furthermore, the vertical trenches 104 for channeling the hydrogen molecules require an additional process mask. Moreover, the oxide layer 103 for bonding the two regions 101 and 102 is an additional process fabrication step. The plasma activation and BCB processes add to the overall cost of fabricating high volume hybrid III-V silicon lasers.